On the widespread enhancement in fine particulate matter across the Indo-Gangetic Plain towards winter

Abstract

Fine particulate matter (PM 2.5 , aerodynamic diameter ≤2.5 µm) impacts the climate, reduces visibility and severely influences human health. The Indo-Gangetic Plain (IGP), home to about one-seventh of the world's total population and a hotspot of aerosol loading, observes strong enhancements in the pM 2.5 concentrations towards winter. We performed high-resolution (12 km × 12 km) atmospheric chemical transport modeling (WRF-Chem) for the post-monsoon to winter transition to unravel the underlying dynamics and influences of regional emissions over the region. Model, capturing the observed variations to an extent, reveals that the spatial distribution of PM 2.5 having patches of enhanced concentrations (≥100 µgm −3) during post-monsoon, evolves dramatically into a widespread enhancement across the IGP region during winter. A sensitivity simulation, supported by satellite observations of fires, shows that biomass-burning emissions over the northwest IGP play a crucial role during post-monsoon. Whereas, in contrast, towards winter, a large-scale decline in the air temperature, significantly shallower atmospheric boundary layer, and weaker winds lead to stagnant conditions (ventilation coefficient lower by a factor of ~4) thereby confining the anthropogenic influences closer to the surface. Such changes in the controlling processes from post-monsoon to winter transition profoundly affect the composition of the fine aerosols over the IGP region. The study highlights the need to critically consider the distinct meteorological processes of west-to-east IGP and changes in dominant sources from post-monsoon to winter in the formulation of future pollution mitigation policies.

Exceedances and trends of particulate matter (PM2.5) in five Indian megacities

“…Hyderabad, an inland city located in the south-central part of India, has a population of over 7 million people. Delhi and Kolkata are also in the Indo Gangetic plains (IGP), which is one of the most polluted regions of India ( Ojha et al, 2020 ).…”

Impacts of COVID-19 on Air Quality in India

“…West Bengal, and Odisha, they were predominantly more due to the dense population and industries. Also, these states are the part of the IGP corridor where frequent stagnant meteorological conditions favor the accumulation of pollutants in the atmosphere (Dekker et al, 2019;Sawlani et al, 2019;Ojha et al, 2020;Kanawade et al, 2020).…”

PM2.5 diminution and haze events over Delhi during the COVID-19 lockdown period: an interplay between the baseline pollution and meteorology

“…Northern Indian winters experience severe widespread air pollution attributed to a variety of emissions being confined near the surface under stagnant metrological conditions [7][8][9] . Aerosol emissions in India is dominated by transportation, industrial, residential energy usage and biomass burning [10][11][12] .…”